Coronaviruses are prevalent agents of human and animal disease which have a unique replication strategy and distinctive biological characteristics. Many of the features of coronavirus replication and pathogenicity are determined by the two viral envelope glycoproteins. E1 is an o-glycosylated highly hydrophobic glycoprotein which is functionally analogous to the M proteins of other enveloped viruses. E1 interacts with the viral nucleocapsid and determines the intracellular budding site of coronaviruses. The peplomers are formed of the larger glycoprotein E2 which binds to host cell receptors and mediates virus-induced cell fusion. E2 contains the neutralization and strain-specific epitopes, and is responsible for the pH-dependent thermolability of coronaviruses. We will analyze the biologically active sites in these glycoproteins. We will compare the amino acid sequence at the E2 cleavage site produced during replication in different hosts or by different enzymes in vitro. Monoclonal antibodies and synthetic peptides will be used to probe the functions of this site and nearby hydrophobic domains which may mediate cell fusion. Monoclonal antibody-resistant mutants will be analyzed to reveal the relationship between changes in the cleavage region and alterations in virus infectivity or pathogenicity. We will map neutralization and strain-specific epitopes on peptide fragments and analyze the effects of glycosylation on the recognition of antigenic determinants. Structural determinants of E1 which may be important in virus assembly and the construction of the viral envelope will be studied using defined peptide fragments obtained by site-specific chemical cleavage. E1 and E2 mutants and revertants will be characterized in detail, including sequencing at the nucleotide level, to probe glycoprotein function in virus replication and pathogenesis.